1. Field of the Disclosure
The present disclosure relates generally to image forming devices and more particularly to a magnetic roll for a dual component development electrophotographic image forming device.
2. Description of the Related Art
Dual component development electrophotographic image forming devices include one or more reservoirs that store a mixture of toner and magnetic carrier beads (the “developer mix”). Toner is electrostatically attracted to the carrier beads as a result of triboelectric interaction between the toner and the carrier beads. A magnetic roll includes a stationary core having one or more permanent magnets and a sleeve that rotates around the core. The magnetic roll attracts the carrier beads in the reservoir having toner thereon to the outer surface of the sleeve through the use of magnetic fields from the core. A photoconductive drum in close proximity to the sleeve of the magnetic roll is charged by a charge roll to a predetermined voltage and a laser selectively discharges areas on the surface of the photoconductive drum to form a latent image on the surface of the photoconductive drum. The sleeve is electrically biased to facilitate the transfer of toner from the developer mix on the outer surface of the sleeve to the discharged areas on the surface of the photoconductive drum forming a toner image on the surface of the photoconductive drum. The photoconductive drum then transfers the toner image, directly or indirectly, to a media sheet forming a printed image on the media sheet.
As the developer mix on the outer surface of the sleeve approaches the photoconductive drum by rotation of the sleeve, the developer mix is trimmed to a desired mass on the magnetic roll by a trim bar. A gap between the trim bar and the outer surface of the sleeve (the “trim bar gap”) dictates how much developer mix is allowed to pass on the outer surface of the sleeve from the reservoir toward the photoconductive drum. The developer mix tends to accumulate and for a shear zone in the reservoir upstream from the trim bar gap. Friction between the outer surface of the sleeve and the developer mix is required to move the developer mix through the shear zone and the trim bar gap to the photoconductive drum.
The magnetic roll sleeve often includes a textured or roughened outer surface in order to provide the desired amount of friction between the outer surface of the sleeve and the developer mix. For example, the outer surfaces of some magnetic roll sleeves are grit blasted. Other magnetic roll sleeves include a series of grooves that extend axially along the length of the sleeve and are equally spaced circumferentially from each other about the outer surface of the sleeve. Some grooved magnetic roll sleeves include a groove density of about 1.27 grooves/mm of the circumference of the outer surface of the sleeve (e.g., 100 grooves on a sleeve having an outer diameter of 25 mm or 80 grooves on a sleeve having an outer diameter of 20 mm). Some larger magnetic roll sleeves, on the order of 62.5 mm in outer diameter, include a knurled outer surface having a sinusoidal, washboard-like knurl pattern that is present on the outer surface of the sleeve at a density of between about 1 and about 1.25 indentations/mm of the circumference of the outer surface of the sleeve. These knurled magnetic roll sleeves have a relatively large circumferential spacing between indentations of between about 0.8 mm and about 1 mm (measured from the center of the trough of one indentation to the center of the trough of the neighboring indentation). These knurled magnetic roll sleeves also have a high (e.g., much greater than 0.1 mm) total indicated runout, a measure of how concentric the sleeve is along its axial length.
Buildup of toner on the outer surface of the sleeve over the life of the magnetic roll tends to increase the amount of friction between the outer surface of the sleeve and the developer mix thereby allowing more developer mix to pass through the trim bar gap and increasing the mass of developer mix on the magnetic roll. Excessive mass of developer mix on the magnetic roll may lead to high rates of carrier bead and toner loss thereby decreasing the life of a replaceable unit holding the reservoir(s) and increasing the operating cost of the image forming device for the user. Accordingly, a magnetic roll sleeve that provides sufficient and consistent friction between the outer surface of the sleeve and a developer mix over the life of the magnetic roll is desired.